Apparatus and method for continuously producing carbon nanotubes

ABSTRACT

Disclosed are an apparatus and method for continuously producing carbon nanotubes. More specifically, disclosed are an apparatus for continuously producing carbon nanotubes including i) a reactor to synthesize carbon nanotubes, ii) a separator to separate a mixed gas from the carbon nanotubes transferred from the reactor, iii) a filter to remove all or part of one or more component gases from the separated mixed gas, and iv) a recirculation pipe to recirculate the filtered mixed gas to the reactor for carbon nanotubes. 
     Advantageously, the apparatus and method for continuously producing carbon nanotubes enable rapid processing, exhibit superior productivity and excellent conversion rate of a carbon source, significantly reduce production costs, reduce energy consumption due to decrease in reactor size relative to capacity, and generate little or no waste gas and are thus environmentally friendly.

TECHNICAL FIELD

The present invention relates to an apparatus and method forcontinuously producing carbon nanotubes. More specifically, the presentinvention relates to an apparatus for continuously producing carbonnanotubes which enables rapid processing, exhibits superior productivityand excellent conversion rate of a carbon source, significantly reducesproduction costs, reduces energy consumption due to decrease in reactorsize relative to capacity, and generates little or no waste gas and isthus environmentally friendly, and a method for continuously producingcarbon nanotubes using the apparatus.

BACKGROUND ART

Carbon nanotubes (hereinafter, referred as to ‘CNT’) are generallyprepared by arc discharge, laser ablation, chemical vapor deposition orthe like.

However, the arc discharge and laser ablation are disadvantageouslydifficult to mass-produce, and involve excessive preparation costs andpurchase costs of a laser apparatus.

Furthermore, chemical vapor deposition has problems in that a synthesisrate is very slow and CNT particles that are synthesized are excessivelysmall in the case of using a vapor dispersion catalyst and there is alimit to mass production of CNT because a space use efficiency in thereactor is significantly reduced in the case of using asubstrate-supported catalyst.

Improved methods for mass-producing CNT have been disclosed and examplesthereof include a rotary kiln method for producing CNT by incorporatinga catalyst in a rotating drum reactor and then adding a reaction gasthereto, and a method for synthesizing CNT using a fluidized bed reactorincluding forming a fluidized bed, in which a fluid medium flows whenheated, in a reactor, and synthesizing CNT in the fluidized bed.

However, in accordance with these CNT mass-production methods, areactive gas containing hydrocarbon gas, inert dilute gas and reducinggas to control CNT production reactions at high temperatures isincorporated in a reactor and a carbon source is thus converted into CNTand consumed in the reactor to produce double reducing gas (specificexample, hydrogen gas) as a by-product. Accordingly, there is a need fora technical method to control a mix ratio of these gases to apredetermined level.

However, conventional methods using rotary kiln reactors and fluidizedbed reactors have problems in that a conversion ratio of carbon sourceis at most 80%, in particular, the mixed gas emitted from the reactor isinevitably directly incinerated and the cost of raw materials is thusincreased due to absence of a method for selectively disposing of thereducing gas produced as a byproduct, unit productivity is limited dueto excessive equipment scale, and a great amount of carbon dioxide isemitted during incineration of waste gas.

DISCLOSURE Technical Problem

Therefore, the present invention has been made in view of the aboveproblems, and it is one object of the present invention to provide anapparatus for continuously producing carbon nanotubes which enablesrapid processing, exhibits superior productivity and high conversionrate of a carbon source, significantly reduces production costs, reducesenergy consumption due to decrease in reactor size relative to capacity,and generates little or no waste gas and is thus environmentallyfriendly, and a method for continuously producing carbon nanotubes usingthe apparatus.

The above and other objects can be accomplished by the present inventiondescribed below.

Technical Solution

In accordance with an aspect of the present invention, the above andother objects can be accomplished by the provision of an apparatus forcontinuously producing carbon nanotubes, including i) a reactor tosynthesize carbon nanotubes; ii) a separator to separate a mixed gasfrom the carbon nanotubes transferred from the reactor; iii) a filter toremove all or part of one or more component gases from the separatedmixed gas; and iv) a recirculation pipe to recirculate the filteredmixed gas to the reactor for carbon nanotubes.

In accordance with another aspect of the present invention, provided isa method for continuously producing carbon nanotubes including: i)reacting a reaction gas containing a carbon source, a reducing gas, andan inert gas with a catalyst to synthesize carbon nanotubes; ii)separating a mixed gas discharged along with the synthesized carbonnanotubes; iii) filtering the separated mixed gas to remove the reducinggas produced during the reaction i); and iv) recirculating the filteredmixed gas to the reaction i).

Advantageous Effects

The present invention advantageously provides an apparatus forcontinuously producing carbon nanotubes which enables rapid processing,exhibits superior productivity and excellent conversion rate of a carbonsource, significantly reduces production costs, reduces energyconsumption due to decrease in reactor size relative to capacity, andgenerates little or no waste gas and is thus environmentally friendly,and a method for continuously producing carbon nanotubes using theapparatus.

DESCRIPTION OF DRAWINGS

The above and other objects, features and advantages of the presentinvention will become apparent from the following description ofpreferred embodiments given in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a process view illustrating a continuous CNT productionapparatus including a hydrogen PSA unit according to an embodiment ofthe present invention; and

FIG. 2 is a process view illustrating a continuous CNT productionapparatus provided with a gas separation unit including a metal membrane(hereinafter, referred to as a “metal membrane gas separation unit”)according to an embodiment of the present invention.

BEST MODE

Hereinafter, the present invention will be described in detail.

The present invention provides an apparatus for continuously producingcarbon nanotubes, including i) a reactor to synthesize carbon nanotubes;ii) a separator to separate a mixed gas from the carbon nanotubestransferred from the reactor; iii) a filter to remove all or part of oneor more component gases from the separated mixed gas; and iv) arecirculation pipe to recirculate the filtered mixed gas to the reactorfor the carbon nanotubes.

The carbon nanotube reactor i) may be a chemical vapor depositionreactor, preferably a fluidized bed reactor (hereinafter, referred to asan ‘FBR’), a fixed bed reactor, or a rotary reactor, more preferably arotary kiln type reactor or a fluidized bed reactor, and most preferablya fluidized bed reactor. The fluidized bed reactor has advantagesexcellent productivity and easy CNT mass-production, as compared withreactor volume.

The fluidized bed reactor preferably produces CNTs by feeding a carbonsource, a reducing gas, an inert gas and the like through a reaction gasfeed pipe to a reactor from bottom to top and bringing the gases intocontact with a catalyst injected to the reactor through a catalyst gasfeed pipe in the upper part of the reactor to induce reaction betweenthe gases and the catalyst.

Any reaction gas feed pipe may be used without particular limitation solong as it is generally useful for CNT production apparatuses.Specifically, the reaction gas feed pipe may be a gas distributor or thelike.

Any catalyst feed pipe may be used without particular limitation so longas it is generally useful for CNT production apparatuses. Specifically,the catalyst feed pipe may be a hopper or the like.

The catalyst may be a heterogeneous catalyst having a complex structurecontaining an active metal and a support material commonly used for theproduction of CNT. More specifically, the catalyst may be a supportedcatalyst, a co-precipitation catalyst or the like.

In a case where a supported catalyst is used as a preferred catalyst,the supported catalyst advantageously has a higher bulk density than aco-precipitation catalyst and reduces a possibility of production offine powder by attrition that may be generated in a fluidizing processdue to small amount of fine powder of 10 microns or less unlike theco-precipitation catalyst, and exhibits superior mechanical strength andthus enables the reactor to stably operate.

In a case where a co-precipitation catalyst is used as a preferredcatalyst, the co-precipitation catalyst has advantages of simplepreparation method, merits in terms of preparation costs owing to lowprice of preferred metallic salts as catalyst materials and highcatalyst activity due to wide specific surface area.

The inert gas may be nitrogen (N₂), argon (Ar), or the like.

For example, the fluidized bed reactor may operate as follows. Afluidized bed is formed in the reactor, a catalyst contacts a reactiongas in the fluidized bed to cause reaction, CNTs are grown on anactivated metal of the catalyst, as the reaction progresses, and arethen discharged from the reactor when a bulk density of the productdecreases.

The bulk density may be 0.03 to 0.3 g/cm³, and preferably 0.01 to 0.1g/cm³.

The fluidization velocity of the fluidized bed formed in the fluidizedbed reactor is preferably 0.03 to 30 cm/s, and more preferably 0.1 to 25cm/s.

The minimum fluidization velocity of the fluidized bed in the fluidizedbed reactor is preferably 0.03 to 15 cm/s, and more preferably 1 to 10cm/s.

The rotary kiln reactor or the fluidized bed reactor may be connected toa catalyst supply pipe to supply the catalyst, a reaction gas supplypipe to supply a carbon source, a reducing gas and an inert gas, and aproduct discharge pipe to discharge produced carbon nanotubes and themixed gas containing a reaction byproduct gas.

The carbon source is a carbon-containing gas that may be degraded whenheated and specific examples thereof include aliphatic alkanes,aliphatic alkenes, aliphatic alkynes and aromatic compounds. Morespecifically, examples thereof include methane, ethane, ethylene,acetylene, ethanol, methanol, acetone, carbon monoxide, propane, butane,benzene, cyclohexane, propylene, butene, isobutene, toluene, xylene,cumene, ethylbenzene, naphthalene, phenanthrene, anthracene,formaldehyde, acetaldehyde and the like. Preferred are methane (CH₄),ethane (C₂H₆), carbon monoxide (CO), acetylene (C₂H₂), ethylene (C₂H₄),propylene (C₃H₆), butane (C₄H₁₀) and liquefied petroleum gas (LPG) as amixture.

The separator ii) is not specifically limited so long as it is a tool,equipment or apparatus which is capable of separating the mixed gas fromCNT and is preferably a cyclone.

The filter iii) is not specifically limited so long as it is a material,equipment, machine, tool or apparatus which is capable of selectivelyseparating or removing the mixed gas.

The filter iii) may independently separate the un-reacted carbon source,reducing gas and inert gas from the mixed gas discharged from theseparator and may then selectively transfer the required amount of eachgas to the recirculation pipe.

The filter iii) may remove a predetermined amount of reducing gas fromthe mixed gas discharged from the separator and then transfer thefiltered mixed gas to the recirculation pipe.

The reducing gas may be hydrogen.

The filter iii) is preferably a metal membrane gas separation unit or agas pressure swing adsorption unit which is capable of selectivelyseparating or removing one or more gas components from the mixed gas.

Preferably, the filter iii) may be a gas pressure swing adsorption (PSA)unit.

The gas pressure swing adsorption (PSA) unit is preferably an adsorptiontower or adsorption column (hereinafter, referred to as an “adsorptiontower) which adsorbs a predetermined amount of specific gas whenpressurized and emits the specific gas when depressurized.

In addition, the filter iii) is preferably a hydrogen gas pressure swingadsorption (PSA) unit.

The hydrogen gas pressure swing adsorption (PSA) unit is preferably anadsorption tower which adsorbs a predetermined amount of hydrogen gaswhen pressurized and emits the adsorbed hydrogen gas when depressurized.

For reference, it can be confirmed that inputs of ethylene, hydrogen andnitrogen are reduced by 20 to 30%, 99% and 98%, respectively, ascompared with an output of CNTs, when the CNT particles and mixed gasproduced in the reactor pass through a heat exchanger and are thencooled, the CNT particles and mixed gas are separated from each otherusing a cyclone, and the separated CNT particles are sent to a collectorand then collected, while the mixed gas passes through the hydrogen PSAunit and is then re-circulated.

The PSA unit preferably includes two or more adsorption towers, morepreferably 2 to 6 adsorption towers. In this case, there are advantagesin terms of continuous processing, control of adsorption amount andselective gas separation.

Preferably, the PSA unit is designed to adsorb a specific gas bypressurizing an adsorption tower through which the mixed gas passes and,at the same time, to emit the specific gas by depressurizing theadsorption tower in which the mixed gas is not passed and a specific gasis adsorbed.

Preferably, the adsorption towers are designed to alternately repeatedlyundergo pressurization and depressurization and thereby facilitate thecontinuous process.

Preferably, the PSA unit includes a first fluid direction controller todirect the mixed gas discharged from the separator to the adsorptiontower to perform pressurization, a second fluid direction controller todirect the filtered mixed gas to the recirculation pipe and a thirdfluid direction controller to direct a specific gas discharged from thedepressurized adsorption tower to a discharge gas disposal or storageunit.

The PSA unit preferably includes a connector to connect the first tothird fluid direction controllers.

Preferably, the filter iii) may be a metal membrane gas separation unit.

The metal membrane gas separation unit selectively separates hydrogen ata temperature lower than 500° C. and the metal membrane is selected fromPd, Ir, Rh, Pd—Ni alloys, Pd—Ag alloys and Pd—Cu alloys, andcombinations thereof. Of these, Pd and Pd alloys are preferred, althoughthe metal membrane is not limited thereto.

The metal membrane may be used in plural. The use of one to four metalmembranes may be advantageous in terms of continuous processing, controlof adsorption amount and control of recirculated and suppliedcomposition. However, Pd and Pd alloys having high separation efficiencycan be filtered through a single membrane, and the pressure and supplyamount thereof can be controlled through a separation unit.

For reference, it can be seen confirmed that inputs of ethylene,hydrogen and nitrogen are decreased by 20 to 30%, 99% and 98%,respectively, as compared with an output of CNTs, when the CNT particlesand mixed gas produced in the reactor pass through a heat exchanger andare then cooled, the CNT particles and mixed gas are separated from eachother using a cyclone, and the CNT particles are sent to a collector andthen collected, while the mixed gas passes through the metal membranegas separation unit and is then re-circulated.

The fluidized bed reactor is connected to a reactive gas supply pipe 1,through which a carbon source, a reducing gas, an inert gas or the likeare supplied, and preheats the gases at about 200 to about 500° C. usinga pre-heater 100 and contact-reacts the gases with a catalyst suppliedfrom bottom to top in the reactor 200 through a catalyst supply pipearranged in an upper region to produce CNTs.

A part of specific gas (such as a part of H₂, un-reacted carbon source,N₂ and other inert gases, additional gases such as NH₃ or H₂O) emittedfrom the adsorption tower may be supplied to the recirculation pipe orreactive gas supply pipe, as necessary, in particular, when the specificgas in the filtered mixed gas is deficient.

The unreacted carbon source contained in the mixed gas is preferablycontrolled to 2 to 30% of carbon source supplied to the reactor, morepreferably 5 to 20%.

The CNT production apparatus realizes ideal process operation which hassubstantially constant composition rate and amount, since only acatalyst and the carbon source consumed in the reactor are injectedtherein.

The CNT production apparatus can selectively recirculate the mixed gascontaining the un-reacted carbon source, the inert gas, the byproductgas, and the like that have been generally incinerated or dischargedusing conventional a flare stack, incinerator or the like to secure atleast 98% of a carbon source conversion rate without additionallyinjecting any inert gas. Accordingly, the CNT production apparatussignificantly reduces CNT production costs, eliminates the necessity ofincineration, is free of a problem in which carbon dioxide is releasedto the atmosphere and thus realizes an environmentally friendly process.

In addition, the CNT production apparatus can significantly decrease thesize of the fluidized bed as compared with capacity of low-energyconsumption equipment and thus energy cost of the fluidized bed reactorwhich operates at 600 to 1,000° C.

For the CNT production apparatus, the heat exchanger may be connectedbetween the reactor and the separator or between the separator and CNTcollector and, preferably, may be connected between the reactor and theseparator.

The expression “between the reactor and the separator” includes theinside of the reactor and a filter may be arranged in an expander partof the fluidized bed reactor along with the heat exchanger.

When the reactor is designed to collect CNTs synthesized in the reactorat the bottom part of the reactor, the filter may be installed in thereaction apparatus to remove fine powders contained in the mixed gasthat is discharged at the upper part thereof, and also when the heatexchanger is provided in the reaction apparatus, the separator, such ascyclone, may be also arranged in the reaction apparatus.

The component gas of the filter iii) may be a byproduct gas produced inthe reactor i).

The continuous CNT production apparatus preferably further includes acontrol unit to control the amount of the reaction gas supplied to thereactor and the amount of component gas removed in the filter.

The control unit may control the amount of the reducing gas supplied tothe reactor and the amount of the reducing gas passing through thefilter.

The control unit may ensure that the amount of the reducing gas suppliedto the reactor is equivalent to the amount of the reducing gas passedthrough the filter.

The continuous CNT production apparatus preferably further includes afilter, a scrubber or a combination thereof arranged between theseparator ii) and the filter iii).

The filter collects CNT particles remaining in the mixed gas separatedby the separator, and the scrubber removes harmful materials, such ashalides, present in the mixed gas separated by the separator.

The continuous CNT production apparatus preferably further includes apre-heater to preheat the reactive gas before the reactive gas isinjected into the reactor.

The continuous CNT production apparatus considerably increasesproduction cost saving, since injection of a greater amount of inert gasand a reducing gas in an amount equivalent to or greater than the amountof carbon source is required, as the reactor size increases.

The continuous CNT production apparatus may not include a waste gasincineration unit such as a flare stack, incinerator or the like.

The method for continuously producing carbon nanotubes according to thepresent invention comprises: i) reacting a reaction gas containing acarbon source, a reducing gas, and an inert gas with a catalyst tosynthesize carbon nanotubes; ii) separating a mixed gas discharged alongwith the synthesized carbon nanotubes; iii) filtering the separatedmixed gas to remove all or part of the reducing gas produced during thereaction i); and iv) recirculating the filtered mixed gas to thereaction i).

The amount of reducing gas that is removed in the filtration iii)preferably corresponds to the amount of reducing gas produced in thereaction i).

The molar ratio of the carbon source to the reducing gas is preferably1:0.5 to 1:10, more preferably 1:0.9 to 1:6, and most preferably 1:1 to1:5. Within this range, there is an effect of suppressing production ofamorphous carbon through controlling the production rate of carbonnanotubes and thereby increasing the production of graphitic carbon.

In the process of producing CNTs i), if necessary, one or more selectedfrom the group consisting of water, ammonia, NO, NO₂, and the like canbe further injected.

As a specific example, the catalyst may be produced by dissolving acatalyst-active metal precursor such as Co(NO₃)₂-6H₂O,(NH₄)₆Mo₇O₂₄-4H₂O, Fe(NO₃)₂-6H₂O, Ni(NO₃)₂-6H₂O or the like in distilledwater and wet impregnating the solution in a carrier such as Al(OH)₃,Mg(NO₃)₂, or colloidal silica.

In addition, the catalyst may be produced by treating a catalyst activemetal precursor and a carrier such as Al(OH)₃, Mg(NO₃)₂, or colloidalsilica with ultrasonic waves.

In addition, the catalyst may be produced by a sol-gel method using achelating agent, such as citric acid, ethylenediaminetetraacetic acid(EDTA) etc., to smoothly dissolve catalyst active metal precursor, ormay be produced by co-precipitating a catalyst active metal precursorwell soluble in water.

The filtration iii) may be carried out by a separation method, unit ordevice which is capable of selectively separating the mixed gas.

Preferably, the filtration iii) may be carried out using a gas pressureswing adsorption (PSA) unit.

Preferably, the reducing gas is hydrogen and the gas PSA unit is a PSAunit.

Preferably, the filtration iii) may be carried out using a metalmembrane gas separation unit.

The metal membrane gas separation unit selectively separates hydrogen ata temperature lower than 500° C. and the metal membrane is selected fromPd, Ir, Rh, Pd—Ni alloys, Pd—Ag alloys, Pd—Cu alloys and combinationsthereof. Of these, Pd and Pd alloys are preferred, although the metalmembrane is not limited thereto.

The continuous CNT production method may further include injecting acarbon source in an amount consumed in the reaction i) to the filteredmixed gas in the recirculation iv).

The continuous CNT production method may not include incinerating thewaste gas.

A specific example of the continuous CNT production apparatus accordingto the present invention is schematically shown in FIGS. 1 and 2. Onlythe device required for describing the present invention is shown andother devices, including any pump, additional valve, pipe etc., that arerequired for performing the present method are excluded in FIGS. 1 and2.

Hereinafter, although the preferred embodiments of the present inventionwill be disclosed for illustrative purposes, those skilled in the artwill appreciate that various modifications, additions and substitutionsare possible, without departing from the scope and spirit of theinvention as disclosed in the accompanying claims.

EXAMPLES Example 1 Preparation of CNT Catalyst

A flask A containing 200 ml of an aqueous solution of 37.039 g ofCo(NO₃)₂-6H₂O and a flask B containing 200 ml of an aqueous solution of32.30 g of (NH₄)₆Mo₇O₂₄-4H₂O were prepared. Then, the solutions presentin the flasks A and B were sequentially or simultaneously added to aflask C containing 50 g of Al₂O₃ (D50=76 micron, pore volume: 0.64cm³/g, surface area: 237 m²/g, available from Saint Gobain Corporation),and a catalyst active metal precursor was then sufficiently supported onAl₂O₃, while stirring for 60 minutes or longer. Then, the resultingproduct was vacuum-filtered through a 10 micron filter paper or 4× glassfilter to separate a filter cake in which the catalyst active metalprecursor was supported and the filter cake was washed with distilledwater and then collected. The collected filter cake was dried in an ovenat 120° C. for 24 hours. The dried catalyst was fired for 3 hours at600° C. to prepare a CNT catalyst.

<Production of CNTs>

5 g of the CNT catalyst was supplied to the top of a dispersion plate(in the form of a bubble cap or sieve) of a vertical fluidized bedreactor having a diameter of 55 mm and a height of 1 m, a reaction gas(C₂H₄:H₂:N₂=1:1:1) was injected into the reactor at a rate of 3,000ml/min through a reaction gas supply pipe connected to the bottom partof the reactor and CNTs were synthesized at 800° C. for one hour.

The CNT production reaction was performed as a continuous reaction byseparating a mixed gas (un-reacted carbon source, C₂H₄, inert gas, N₂,initially injected reducing gas, H₂, and H₂ produced as a byproduct)from the CNT product through a cyclone, selectively separating anddischarging 30% of hydrogen gas from the mixed gas through a hydrogenPSA unit (two columns, each filled with 100 mL of Zeolite 5A) serving asa filter, and recirculating the filtered mixed gas (un-reacted C₂H₄, N₂and H₂) through the recirculation pipe to the reaction gas supply line.

After one hour of reaction, CNTs collected in the CNT collector had ayield [(weight of CNTs collected−weight of catalyst injected)/weight ofcatalyst injected×100] of 950%, based on catalyst input.

Example 2

CNTs were produced in the same manner as in Example 1, except that thecomposition of the reaction gas was changed to C₂H₄:H₂:N₂=1:2:1 and 35%of the hydrogen gas discharged from the reactor was selectivelyseparated and discharged in the hydrogen PSA unit.

The reaction can be safely carried out by selectively removing only H₂produced as a byproduct and recirculating the mixed gas consisting ofthe remaining H₂ and N₂, and 4.8% of un-reacted C₂H₄ to the reaction gassupply pipe. In addition, the amounts of H₂ and N₂ used were minimizedby reacting without an additional supply of H₂ and N₂ by performing acontinuous operation through adding only C₂H₄ corresponding to 85% ofthe initial feed amount to the reaction gas supply pipe.

After one hour of reaction, CNTs collected in the CNT collector had ayield of 1,020%, based on catalyst input.

Example 3

CNTs were produced in the same manner as in Example 1, except that thecomposition of the reaction gas was changed to C₂H₄:H₂:N₂=1:3:1 and 29%of the hydrogen gas discharged from the reactor was selectivelyseparated and discharged in the hydrogen PSA unit.

The reaction can be safely carried out by selectively removing only H₂produced as a byproduct and recirculating the mixed gas consisting ofthe remaining H₂ and N₂, and 3.6% of un-reacted C₂H₄ to the reaction gassupply pipe. In addition, the amounts of H₂ and N₂ used were minimizedby reacting without an additional supply of H₂ and N₂ by performing acontinuous operation through adding only C₂H₄ corresponding to 85% ofthe initial feed amount to the reaction gas supply pipe.

After one hour of reaction, CNTs collected in the CNT collector had ayield of 780%, based on catalyst input.

Example 4

CNTs were produced in the same manner as in Example 1, except that thecomposition of the reaction gas was changed to C₂H₄:H₂:N₂=1:4:1 and 24%of the hydrogen gas discharged from the reactor was selectivelyseparated and discharged in the hydrogen PSA unit.

The reaction can be safely carried out by selectively removing only H₂produced as a byproduct and recirculating the mixed gas consisting ofthe remaining H₂ and N₂, and 3.3% of un-reacted C₂H₄ to the reaction gassupply pipe. In addition, the amounts of H₂ and N₂ used were minimizedby reacting without an additional supply of H₂ and N₂ by performing acontinuous operation through adding only C₂H₄ corresponding to 83% ofthe initial feed amount to the reaction gas supply pipe.

After one hour of reaction, CNTs collected in the CNT collector had ayield of 630%, based on catalyst input.

Example 5

CNTs were produced in the same manner as in Example 1, except that thecomposition of the reaction gas was changed to C₂H₄:H₂:N₂=1:5:1 and 20%of the hydrogen gas discharged from the reactor was selectivelyseparated and discharged in the hydrogen PSA unit.

The reaction can be safely carried out by selectively removing only H₂produced as a byproduct and recirculating the mixed gas consisting ofthe remaining H₂ and N₂, and 3.2% of un-reacted C₂H₄ to the reaction gassupply pipe. In addition, the amounts of H₂ and N₂ used were minimizedby reacting without an additional supply of H₂ and N₂ by performing acontinuous operation through adding only C₂H₄ corresponding to 80% ofthe initial feed amount to the reaction gas supply pipe.

After one hour of reaction, CNTs collected in the CNT collector had ayield of 580%, based on catalyst input.

Example 6

3 g of the CNT catalyst prepared in Example 1 above was charged into a15 cm cylindrical reaction module, both sides of which were supported bya protruded ring structure and were composed of a 10 micron mesh,arranged in a rotary drum reactor having a diameter of 55 mm and aheight of 60 cm, and then supplied through the catalyst gas supply pipeto the reactor. The reaction gas (C₂H₄:H₂:N₂=1:1:1) was added to thereactor at a rate of 1,500 ml/min through the reaction gas supply pipe.The reactor was tilted at an angle of 30 degrees and rotated at a rateof 30 rpm. The reaction was progressed for 60 minutes at 800° C. tosynthesize CNTs.

The CNT production reaction was performed as a continuous reaction byseparating a mixed gas (un-reacted carbon source, C₂H₄, inert gas, N₂,initially injected reducing gas, H₂, and H₂ produced as a byproduct)from the CNT product through a cyclone, selectively separating anddischarging 35% of hydrogen gas from the mixed gas through a hydrogenPSA unit (two columns, each filled with 1,000 mL of Zeolite 5A) servingas a filter, and recirculating the filtered mixed gas (un-reacted C₂H₄,N₂ and H₂) through the recirculation pipe to the reaction gas supplyline.

After one hour of reaction, CNTs collected in the CNT collector had ayield of 1,050%, based on catalyst input.

Example 7

CNTs were produced in the same manner as in Example 6, except that thecomposition of the reaction gas was changed to C₂H₄:H₂:N₂=1:2:1 and 36%of the hydrogen gas discharged from the reactor was selectivelyseparated and discharged in the hydrogen PSA unit.

The reaction can be safely carried out by selectively removing only H₂produced as a byproduct and recirculating the mixed gas consisting ofthe remaining H₂ and N₂, and 4.2% of un-reacted C₂H₄ to the reaction gassupply pipe. In addition, the amounts of H₂ and N₂ used were minimizedby reacting without an additional supply of H₂ and N₂ by performing acontinuous operation through adding only C₂H₄ corresponding to 87% ofthe initial feed amount to the reaction gas supply pipe.

After one hour of reaction, CNTs collected in the CNT collector had ayield of 850%, based on catalyst input.

Example 8

CNTs were produced in the same manner as in Example 6, except that thecomposition of the reaction gas was changed to C₂H₄:H₂:N₂=1:3:1 and 29%of the hydrogen gas discharged from the reactor was selectivelyseparated and discharged in the hydrogen PSA unit.

The reaction can be safely carried out by selectively removing only H₂produced as a byproduct and recirculating the mixed gas consisting ofthe remaining H₂ and N₂ and 3.6% of un-reacted C₂H₄ to the reaction gassupply pipe. In addition, the amounts of H₂ and N₂ used were minimizedby reacting without an additional supply of H₂ and N₂ by performing acontinuous operation through adding only C₂H₄ corresponding to 85% ofthe initial feed amount to the reaction gas supply pipe.

After one hour of reaction, CNTs collected in the CNT collector had ayield of 680%, based on catalyst input.

Example 9

CNTs were produced in the same manner as in Example 6, except that thecomposition of the reaction gas was changed to C₂H₄:H₂:N₂=1:4:1 and 24%of the hydrogen gas discharged from the reactor was selectivelyseparated and discharged in the hydrogen PSA unit.

The reaction can be safely carried out by selectively removing only H₂produced as a byproduct and recirculating the mixed gas consisting ofthe remaining H₂ and N₂, and 3.7% of un-reacted C₂H₄ to the reaction gassupply pipe. In addition, the amounts of H₂ and N₂ used were minimizedby reacting without an additional supply of H₂ and N₂ by performing acontinuous operation through adding only C₂H₄ corresponding to 81% ofthe initial feed amount to the reaction gas supply pipe.

After one hour of reaction, CNTs collected in the CNT collector had ayield of 560%, based on catalyst input.

Example 10

CNTs were produced in the same manner as in Example 6, except that thecomposition of the reaction gas was changed to C₂H₄:H₂:N₂=1:5:1 and 21%of the hydrogen gas discharged from the reactor was selectivelyseparated and discharged in the hydrogen PSA unit.

The reaction can be safely carried out by selectively removing only H₂produced as a byproduct and recirculating the mixed gas consisting ofthe remaining H₂ and N₂, and 3.0% of un-reacted C₂H₄ to the reaction gassupply pipe. In addition, the amounts of H₂ and N₂ used were minimizedby reacting without an additional supply of H₂ and N₂ by performing acontinuous operation through adding only C₂H₄ corresponding to 81% ofinitial feed amount to the reaction gas supply pipe.

After one hour of reaction, CNTs collected in the CNT collector had ayield of 490%, based on catalyst input.

Example 11 Preparation of CNT Catalyst

A flask A containing 300 ml of an aqueous solution of 37.039 g ofCo(NO₃)₂-6H₂O and a flask B containing 300 ml of an aqueous solution of32.30 g of (NH₄)₆Mo₇O₂₄-4H₂O were prepared. Then, the solutions presentin the flasks A and B were added to MgO (particle size: 44 to 106microns, available from Sigma-Aldrich Corp.) and sufficiently supportedin Al₂O₃, while stirring for 60 minutes or longer. Then, the resultingproduct was vacuum-filtered through a 10 micron filter paper to separatea filter cake and the filter cake was washed with distilled water andthen collected. The collected filter cake was dried in an oven at 120°C. for 24 hours. The dried catalyst was fired for 3 hours at 800° C. toprepare a CNT catalyst.

<Production of CNTs>5 g of the CNT catalyst was supplied to the top of adispersion plate of a vertical fluidized bed reactor having a diameterof 55 mm and a height of 1 m, a reaction gas (C₂H₄:H₂:N₂=1:2:1) wasinjected into the reactor at a rate of 3,000 ml/min through a reactiongas supply pipe connected to the bottom part of the reactor and CNTswere synthesized at 800° C. for one hour.

The CNT production reaction was performed as a continuous reaction byseparating a mixed gas (un-reacted carbon source, C₂H₄, inert gas, N₂,initially injected reducing gas, H₂, and H₂ produced as a byproduct)from the CNT product through a cyclone, selectively separating anddischarging 34% of hydrogen gas from the mixed gas through a hydrogenPSA unit (two columns, each filled with 1,000 ml, of Zeolite 5A) servingas a filter, and recirculating the filtered mixed gas (un-reacted C₂H₄,N₂ and H₂) through the recirculation pipe to the reaction gas supplyline.

After one hour of reaction, CNTs collected in the CNT collector had ayield [(weight of CNTs collected−weight of catalyst injected)/weight ofcatalyst injected×100] of 1,030%, based on catalyst input.

Accordingly, the present invention realizes continuous production ofCNTs by supplementing only ethylene deficiency without additionallysupplying N₂ and H₂ among initially added reaction gas components.

Example 12

CNTs were produced in the same manner as in Example 11, except that thecomposition of the reaction gas was changed to C₂H₄:H₂:N₂=1:3:1 and 29%of the hydrogen gas discharged from the reactor was selectivelyseparated and discharged in the hydrogen PSA unit.

The reaction can be safely carried out by selectively removing only H₂produced as a byproduct and recirculating the mixed gas consisting ofthe remaining H₂ and N₂, and 3.8% of un-reacted C₂H₄ to the reaction gassupply pipe. In addition, the amounts of H₂ and N₂ used were minimizedby reacting without an additional supply of H₂ and N₂ by performing acontinuous operation through adding only C₂H₄ corresponding to 84% ofinitial feed amount to the reaction gas supply pipe.

After one hour of reaction, CNT collected in the CNT collector had ayield of 810%, based on catalyst input.

Example 13

CNTs were produced in the same manner as in Example 11, except that thecomposition of the reaction gas was changed to C₂H₄:H₂:N₂=1:4:1 and 24%of the hydrogen gas discharged from the reactor was selectivelyseparated and discharged in the hydrogen PSA unit.

The reaction can be safely carried out by selectively removing only H₂produced as a byproduct and recirculating the mixed gas consisting ofthe remaining H₂ and N₂, and 3.6% of un-reacted C₂H₄ to the reaction gassupply pipe. In addition, the amounts of H₂ and N₂ used were minimizedby reacting without an additional supply of H₂ and N₂ by performing acontinuous operation through adding only C₂H₄ corresponding to 81% ofthe initial feed amount to the reaction gas supply pipe.

After one hour of reaction, CNTs collected in the CNT collector had ayield of 670%, based on catalyst input.

Example 14

CNTs were produced in the same manner as in Example 11, except that thecomposition of the reaction gas was changed to C₂H₄:H₂:N₂=1:5:1 and 21%of the hydrogen gas discharged from the reactor was selectivelyseparated and discharged in the hydrogen PSA unit.

The reaction can be safely carried out by selectively removing only H₂produced as a byproduct and recirculating the mixed gas consisting ofthe remaining H₂ and N₂, and 3.2% of un-reacted C₂H₄ to the reaction gassupply pipe. In addition, the amounts of H₂ and N₂ used were minimizedby reacting without an additional supply of H₂ and N₂ by performing acontinuous operation through adding only C₂H₄ corresponding to 80% ofthe initial feed amount to the reaction gas supply pipe.

After one hour of reaction, CNT collected in the CNT collector had ayield of 560%, based on catalyst input.

Example 15

3 g of the CNT catalyst prepared in Example 11 above was charged into a15 cm cylindrical reaction module, both sides of which were supported bya protruded ring structure and were composed of a 10 micron mesh,arranged in a rotary drum reactor having a diameter of 55 mm and aheight of 60 cm, and then supplied through the catalyst gas supply pipeto the reactor. The reaction gas (C₂H₄:H₂:N₂=1:1:1) was added to thereactor at a rate of 1,500 ml/min through the reaction gas supply pipe.The reactor was tilted at an angle of 30 degrees and rotated at a rateof 30 rpm. The reaction was progressed for 60 minutes at 800° C. tosynthesize CNTs.

The CNT production reaction was performed as a continuous reaction byseparating a mixed gas (un-reacted carbon source, C₂H₄, inert gas, N₂,initially injected reducing gas, H₂, and H₂ produced as byproduct) fromthe CNT product through a cyclone, selectively separating anddischarging 40% of hydrogen gas from the mixed gas through a hydrogenPSA unit serving as a filter, and recirculating the filtered mixed gas(un-reacted C₂H₄, N₂ and H₂) through the recirculation pipe to thereaction gas supply line.

After one hour of reaction, CNT collected in the CNT collector had ayield of 980%, based on catalyst input.

Example 16

CNTs were produced in the same manner as in Example 15, except that thecomposition of the reaction gas was changed to C₂H₄:H₂:N₂=1:2:1 and 36%of the hydrogen gas discharged from the reactor was selectivelyseparated and discharged in the hydrogen PSA unit.

The reaction can be safely carried out by selectively removing only H₂produced as a byproduct and recirculating the mixed gas consisting ofthe remaining H₂ and N₂, and 3.8% of un-reacted C₂H₄ to the reaction gassupply pipe. In addition, the amounts of H₂ and N₂ used were minimizedby reacting without an additional supply of H₂ and N₂ by performing acontinuous operation through adding only C₂H₄ corresponding to 88% ofthe initial feed amount to the reaction gas supply pipe.

After one hour of reaction, CNTs collected in the CNT collector had ayield of 840%, based on catalyst input.

Example 17

CNTs were produced in the same manner as in Example 15, except that thecomposition of the reaction gas was changed to C₂H₄:H₂:N₂=1:3:1 and 29%of the hydrogen gas discharged from the reactor was selectivelyseparated and discharged in the hydrogen PSA unit.

The reaction can be safely carried out by selectively removing only H₂produced as a byproduct and recirculating the mixed gas consisting ofthe remaining H₂ and N₂, and 2.9% of un-reacted C₂H₄ to the reaction gassupply pipe. In addition, the amounts of H₂ and N₂ used were minimizedby reacting, without an additional supply of H₂ and N₂, by performing acontinuous operation through adding only C₂H₄ corresponding to 88% ofthe initial feed amount to the reaction gas supply pipe.

After one hour of reaction, CNTs collected in the CNT collector had ayield of 690%, based on catalyst input.

Example 18

CNTs were produced in the same manner as in Example 15, except that thecomposition of the reaction gas was changed to C₂H₄:H₂:N₂=1:4:1 and 24%of the hydrogen gas discharged from the reactor was selectivelyseparated and discharged in the hydrogen PSA unit.

The reaction can be safely carried out by selectively removing only H₂produced as a byproduct and recirculating the mixed gas consisting ofthe remaining H₂ and N₂, and 3.3% of un-reacted C₂H₄ to the reaction gassupply pipe. In addition, the amounts of H₂ and N₂ used were minimizedby reacting, without an additional supply of H₂ and N₂, by performing acontinuous operation through adding only C₂H₄ corresponding to 83% ofthe initial feed amount to the reaction gas supply pipe.

After one hour of reaction, CNTs collected in the CNT collector had ayield of 560%, based on catalyst input.

Example 19

CNTs were produced in the same manner as in Example 15, except that thecomposition of the reaction gas was changed to C₂H₄:H₂:N₂=1:5:1 and 21%of the hydrogen gas discharged from the reactor was selectivelyseparated and discharged in the hydrogen PSA unit.

The reaction can be safely carried out by selectively removing only H₂produced as a byproduct and recirculating the mixed gas consisting ofthe remaining H₂ and N₂, and 2.8% of un-reacted C₂H₄ to the reaction gassupply pipe. In addition, the amounts of H₂ and N₂ used were minimizedby reacting, without an additional supply of H₂ and N₂, by performing acontinuous operation through adding only C₂H₄ corresponding to 83% ofthe initial feed amount to the reaction gas supply pipe.

After one hour of reaction, CNTs collected in the CNT collector had ayield of 460%, based on catalyst input.

Example 20 Preparation of CNT Catalyst

A flask A containing 200 ml of an aqueous solution of 54.25 g ofFe(NO₃)₂-6H₂O and a flask B containing 200 ml of an aqueous solution of32.30 g of (NH₄)₆Mo₇O₂₄-4H₂O were prepared. Then, the solutions presentin the flasks A and B were added to 5 g of SiO₂ (D50=55 micron, surfacearea: 550 m²/g, Merck 9385) and a catalyst active metal precursor wassufficiently supported in Al₂O₃, while stirring for 60 minutes orlonger. Then, the resulting product was vacuum-filtered through a 10micron filter paper to separate a filter cake and the filter cake waswashed with distilled water and then collected. The collected filtercake was dried in an oven at 120° C. for 24 hours. The dried catalystwas fired for 3 hours at 800° C. to prepare a CNT catalyst.

<Production of CNTs>

5 g of the CNT catalyst was supplied to the top of a dispersion plate ofa vertical fluidized bed reactor having a diameter of 55 mm and a heightof 1 m (a predetermined amount of catalyst was initially added to thereactor and the catalyst was then continuously further added thereto), areaction gas (C₂H₄:H₂:N₂=1:1:1) was injected into the reactor at a rateof 3,000 ml/min through a reaction gas supply pipe connected to thebottom part of the reactor and CNTs were synthesized at 800° C. for onehour.

The CNT production reaction was performed as a continuous reaction byseparating a mixed gas (un-reacted carbon source C₂H₄, inert gas N₂,initially injected reducing gas H_(er) and H₂ produced as a byproduct)from the CNT product through a cyclone, selectively separating anddischarging 33% of hydrogen gas from the mixed gas through a hydrogenPSA unit (two columns, each filled with 1,000 mL of Zeolite 5A) servingas a filter, and recirculating the filtered mixed gas (un-reacted C₂H₄,N₂ and H₂) through the recirculation pipe to the reaction gas supplyline.

After one hour of reaction, CNTs collected in the CNT collector had ayield [(weight of CNTs collected−weight of catalyst injected)/weight ofcatalyst injected×100] of 940%, based on catalyst input.

The filtered mixed gas was assayed by gas chromatography (GC). As aresult, it could be seen that stable operation was possible bysupplementing only ethylene deficiency without additionally supplying N₂and H₂ among initially added reaction gas components, and CNTs couldthus be continuously produced.

Example 21

CNTs were produced in the same manner as in Example 20, except that thecomposition of the reaction gas was changed to C₂H₄:H₂:N₂=1:3:1 and 27%of the hydrogen gas discharged from the reactor was selectivelyseparated and discharged in the hydrogen PSA unit.

The reaction can be safely carried out by selectively removing only H₂produced as a byproduct and recirculating the mixed gas consisting ofthe remaining H₂ and N₂, and 4.8% of un-reacted C₂H₄ to the reaction gassupply pipe. In addition, the amounts of H₂ and N₂ used were minimizedby reacting without an additional supply of H₂ and N₂, by performing acontinuous operation through adding only C₂H₄ corresponding to 80% ofthe initial feed amount to the reaction gas supply pipe.

After one hour of reaction, CNTs collected in the CNT collector had ayield of 770%, based on catalyst input.

Example 22

CNTs were produced in the same manner as in Example 20, except that thecomposition of the reaction gas was changed to C₂H₄:H₂:N₂=1:4:1 and 23%of the hydrogen gas discharged from the reactor was selectivelyseparated and discharged in the hydrogen PSA unit.

The reaction can be safely carried out by selectively removing only H₂produced as a byproduct and recirculating the mixed gas consisting ofthe remaining H₂ and N₂, and 4.2% of un-reacted C₂H₄ to the reaction gassupply pipe. In addition, the amounts of H₂ and N₂ used were minimizedby reacting without an additional supply of H₂ and N₂ by performing acontinuous operation through adding only C₂H₄ corresponding to 78% ofthe initial feed amount to the reaction gas supply pipe.

After one hour of reaction, CNTs collected in the CNT collector had ayield of 610%, based on catalyst input.

Example 23

CNTs were produced in the same manner as in Example 20, except that thecomposition of the reaction gas was changed to C₂H₄:H₂:N₂=1:5:1 and 19%of the hydrogen gas discharged from the reactor was selectivelyseparated and discharged in the hydrogen PSA unit.

The reaction can be safely carried out by selectively removing only H₂produced as a byproduct and recirculating the mixed gas consisting ofthe remaining H₂ and N₂, and 4.0% of un-reacted C₂H₄ to the reaction gassupply pipe. In addition the amounts of H₂ and N₂ used were minimized byreacting without an additional supply of H₂ and N₂, by performing acontinuous operation through adding only C₂H₄ corresponding to 75% ofthe initial feed amount to the reaction gas supply pipe.

After one hour of reaction, CNTs collected in the CNT collector had ayield of 530%, based on catalyst input.

Example 24

3 g of the CNT catalyst prepared in Example 20 above was charged in a 15cm cylindrical reaction module, both sides of which were supported by aprotruded ring structure and were composed of a 10 micron mesh, arrangedin a rotary drum reactor having a diameter of 55 mm and a height of 60cm, and then supplied through the catalyst gas supply pipe to thereactor. The reaction gas (C₂H₄:H₂:N₂=1:1:1) was added to the reactor ata rate of 1,500 ml/min through the reaction gas supply pipe. The reactorwas tilted at an angle of 30 degrees and rotated at a rate of 30 rpm.The reaction was progressed for 60 minutes at 800° C. to synthesizeCNTs.

The CNT production reaction was performed as a continuous reaction byseparating a mixed gas (un-reacted carbon source, C₂H₄, inert gas, N₂,initially injected reducing gas, H₂, and H₂ produced as byproduct) fromthe CNT product through a cyclone, selectively separating anddischarging 40% of hydrogen gas from the mixed gas through a hydrogenPSA unit serving as a filter, and recirculating the filtered mixed gas(un-reacted C₂H₄, N₂ and H₂) through the recirculation pipe to thereaction gas supply line.

After one hour of reaction, CNTs collected in the CNT collector had ayield of 920%, based on catalyst input.

Example 25

CNTs were produced in the same manner as in Example 24, except that thecomposition of the reaction gas was changed to C₂H₄:H₂:N₂=1:2:1 and 35%of the hydrogen gas discharged from the reactor was selectivelyseparated and discharged in the hydrogen PSA unit.

The reaction can be safely carried out by selectively removing only H₂produced as a byproduct and recirculating the mixed gas consisting ofthe remaining H₂ and N₂, and 4.8% of un-reacted C₂H₄ to the reaction gassupply pipe. In addition, the amounts of H₂ and N₂ used were minimizedby reacting without an additional supply of H₂ and N₂ by performing acontinuous operation through adding only C₂H₄ corresponding to 85% ofthe initial feed amount to the reaction gas supply pipe.

After one hour of reaction, CNTs collected in the CNT collector had ayield of 840%, based on catalyst input.

Example 26

CNTs were produced in the same manner as in Example 24, except that thecomposition of the reaction gas was changed to C₂H₄:H₂:N₂=1:3:1 and 29%of the hydrogen gas discharged from the reactor was selectivelyseparated and discharged in the hydrogen PSA unit.

The reaction can be safely carried out by selectively removing only H₂produced as a byproduct and recirculating the mixed gas consisting ofthe remaining H₂ and N₂, and 3.6% of un-reacted C₂H₄ to the reaction gassupply pipe. In addition, the amounts of H₂ and N₂ used were minimizedby reacting, without an additional supply of H₂ and N₂, by performing acontinuous operation through adding only C₂H₄ corresponding to 85% ofthe initial feed amount to the reaction gas supply pipe.

After one hour of reaction, CNTs collected in the CNT collector had ayield of 670%, based on catalyst input.

Example 27

CNTs were produced in the same manner as in Example 24, except that thecomposition of the reaction gas was changed to C₂H₄:H₂:N₂=1:4:1 and 24%of the hydrogen gas discharged from the reactor was selectivelyseparated and discharged in the hydrogen PSA unit.

The reaction can be safely carried out by selectively removing only H₂produced as a byproduct and recirculating the mixed gas consisting ofthe remaining H₂ and N₂, and 3.5% of un-reacted C₂H₄ to the reaction gassupply pipe. In addition, the amounts of H₂ and N₂ used were minimizedby reacting, without an additional supply of H₂ and N₂, by performing acontinuous operation through adding only C₂H₄ corresponding to 82% ofthe initial feed amount to the reaction gas supply pipe.

After one hour of reaction, CNTs collected in the CNT collector had ayield of 550%, based on catalyst input.

Example 28

CNTs were produced in the same manner as in Example 24, except that thecomposition of the reaction gas was changed to C₂H₄:H₂:N₂=1:5:1 and 20%of the hydrogen gas discharged from the reactor was selectivelyseparated and discharged in the hydrogen PSA unit.

The reaction can be safely carried out by selectively removing only H₂produced as a byproduct and recirculating the mixed gas consisting ofthe remaining H₂ and N₂, and 3.2% of un-reacted C₂H₄ to the reaction gassupply pipe. In addition, the amounts of H₂ and N₂ used were minimizedby reacting without an additional supply of H₂ and N₂, by performing acontinuous operation through adding only C₂H₄ corresponding to 80% ofthe initial feed amount to the reaction gas supply pipe.

After one hour of reaction, CNTs collected in the CNT collector had ayield of 480%, based on catalyst input.

In Examples 1 to 28, a carbon source conversion ratio was 98% or more,when H₂ prepared during the reaction was selectively separated and theremaining mixed gas was then recirculated.

Example 29

In addition, 25 g of an Al₂O₃ metal supported catalyst supported with 15wt % Co and 5 wt % of Mo (pure metal content) prepared in the samemanner as in Example 1 was charged in the reactor. 28.2 gmol/hr ofethylene, 28.2 gmol/hr of nitrogen and 84.7 gmol/hr of hydrogen asreaction gases were injected to the reactor. The temperature wascontrolled at 800° C. and then manipulated to synthesize the desiredCNTs. As a result, 0.502 kg/hr of CNTs were produced in the reactor andethylene of the reaction gas was consumed during the reaction andhydrogen was produced as a byproduct in the inlet of the reactor. Forthis reason, the composition of the gas (mixed gas) was changed and 7.3gmol/hr of the ethylene, 28.2 gmol/hr of the nitrogen, and 126.5 gmol/hrof the hydrogen were discharged from the reactor. The discharged CNTsand mixed gas were separated from each other through the cyclone, onlyhydrogen produced as a byproduct in the reactor was selectivelyseparated and discharged from the mixed gas through the hydrogen PSAunit serving as a filter, and the filtered mixed gas (un-reacted C₂H₄,N₂ and H₂) was resupplied through the recirculation pipe to the reactor.As a result, the amount of ethylene gas supplied to the reactor wasconsiderably decreased to 21 gmol/hr.

Meanwhile, for the mixed gas re-circulated to the inlet of the reactor,it was confirmed that flow rates of ethylene, nitrogen and hydrogen were7.2 gmol/hr, 27.4 gmol/hr and 84.7 gmol/hr, respectively. This meansthat the original feed rate of reaction gas can be considerablydecreased by 26% (ethylene), 98% (nitrogen) and 99% (hydrogen), and theproduction cost of the desired CNTs can be thus significantly reduced,as compared with a conventional case in which the entire amount ofdischarged gas is incinerated.

The following Table 1 shows flow rate and composition of the mixed gasdischarged from the reactor. The following Table 2 shows flow rate andcomposition of the mixed gas discharged from the hydrogen PSA unit.

TABLE 1 Flow of gas (mixed gas) present in reactor Flow of gas presentin reactor 3.63 Nm³/h Hydrogen in feed gas: 78.1% C₂H₄ in feed gas: 4.5% N₂ in feed gas: 17.4% *Flow of gas present in reactor outletcorresponds to a total volume of mixed gas discharged from the reactorand supplied to the filter, as a separation unit.

TABLE 2 Gas present in filter (hydrogen PSA unit) outlet (separated anddischarged hydrogen gas) Hydrogen in product gas: >98.6% (hydrogenrecovery 33.04%) C₂H₄ Residual in product gas:  ~0.2% N₂ Residual inproduct gas:  ~1.2% Flow of hydrogen gas selectively 1.03 Nm³/hseparated through separation unit

Example 30

In addition, 25 g of an Al₂O₃ metal supported catalyst supported with 15wt % Co and 5 wt % of Mo prepared in the same manner as in Example 1 wascharged in the reactor. Ethylene, nitrogen and hydrogen as reactiongases were injected to the reactor at a flow rate of 26.2 gmol/hr, 26.2gmol/hr and 104.7 g mol/hr, respectively. The temperature was controlledat 800° C. and then manipulated to synthesize the desired CNTs. As aresult, 0.502 kg/hr of CNTs were produced in the reactor and ethylene ofthe reaction gas was consumed during the reaction and hydrogen wasproduced as a byproduct in the inlet of the reactor. For this reason,the composition of the gas (mixed gas) was changed and 5.2 gmol/hr ofthe ethylene, 26.2 gmol/hr of the nitrogen, and 146.6 gmol/hr of thehydrogen were discharged from the reactor. The discharged CNT and mixedgas were separated from each other through the cyclone, only hydrogenproduced as a byproduct in the reactor was selectively separated anddischarged from the mixed gas through the hydrogen PSA unit serving as afilter, and the filtered mixed gas (un-reacted C₂H₄, N₂ and H₂) wasresupplied to the reactor through the recirculation pipe. As a result,the amount of ethylene gas supplied to the reactor was considerablydecreased to 21 gmol/hr.

Meanwhile, for the mixed gas re-circulated to the inlet of the reactor,it was confirmed that flow rates of ethylene, nitrogen and hydrogen were5.1 gmol/hr, 25.4 gmol/hr and 104.7 gmol/hr, respectively. This meansthat the original feed amount of reaction gas can be considerablydecreased by 20% (ethylene), 98% (nitrogen), and 99% (hydrogen) and theproduction cost of the desired CNTs can thus be significantly reduced,as compared with a conventional case in which the entire amount ofdischarged gas is incinerated.

The following Table 3 shows flow rate and composition of the mixed gasdischarged from the reactor. The following Table 4 shows flow rate andcomposition of the mixed gas discharged from the hydrogen PSA unit.

TABLE 3 Gas (mixed gas) present in reactor outlet Flow of gas present inreactor 3.99 Nm³/h outlet Hydrogen in feed gas: 82.4% C₂H₄ in feed gas:2.94% N₂ in feed gas: 14.7%

TABLE 4 Filter (hydrogen PSA unit) outlet gas (separated and dischargedhydrogen gas) Hydrogen in product gas: >98.6% (hydrogen recovery 28.6%)C₂H₄ residual in product gas:  ~0.2% N₂ residual in product gas:  ~1.2%Flow of hydrogen gas selectively 0.96 Nm³/h separated through separationunit

Example 31

In addition, 25 g of an Al₂O₃ metal supported catalyst supported with 15wt % Co and 5 wt % of Mo prepared in the same manner as in Example 1 wascharged in the reactor. Ethylene, nitrogen and hydrogen as reactiongases were injected to the reactor at flow rates of 27.5 gmol/hr, 27.5gmol/hr and 137.6 gmol/hr, respectively. The temperature was controlledat 800° C. and then manipulated to synthesize the desired CNTs. As aresult, 0.502 kg/hr of CNTs were produced in the reactor and ethylene ofthe reaction gas was consumed during the reaction and hydrogen wasproduced as a byproduct in the inlet of the reactor. For this reason,the composition of the gas (mixed gas) was changed and ethylene,nitrogen, and hydrogen were discharged from the reactor at flow rates of6.6 gmol/hr, 27.5 gmol/hr and 179.4 gmol/hr, respectively. Thedischarged CNT and mixed gas were separated from each other through thecyclone, only hydrogen produced as a byproduct in the reactor wasselectively separated and discharged from the mixed gas through thehydrogen PSA unit serving as a filter, and the filtered mixed gas(un-reacted C₂H₄, N₂ and H₂) was resupplied through the recirculationpipe to the reactor. As a result, the amount of ethylene gas supplied tothe reactor was considerably decreased to 21 gmol/hr.

Meanwhile, for the mixed gas re-circulated to the inlet of the reactor,it was confirmed that flow rates of ethylene, nitrogen and hydrogen were6.5 gmol/hr, 26.7 gmol/hr and 137.6 gmol/hr, respectively. This meansthat the original feed rate of reaction gas can be considerablydecreased by 24% (ethylene), 98% (nitrogen) and 99% (hydrogen), ascompared with a conventional case in which the entire amount ofdischarged gas is incinerated, and the production cost of the desiredCNTs can thus be significantly reduced.

The following Table 5 shows flow rate and composition of the mixed gasdischarged from the reactor. The following Table 6 shows flow rate andcomposition of the mixed gas discharged from the hydrogen PSA unit.

TABLE 5 Gas (mixed gas) present in reactor outlet Flow of gas present inreactor 4.78 Nm³/h outlet Hydrogen in feed gas: 84.02%  C₂H₄ in feedgas:  3.1% N₂ in feed gas: 12.9%

TABLE 6 Filter (hydrogen PSA unit) outlet gas (separated and dischargedhydrogen gas) Hydrogen in product gas: >98.6% (hydrogen recovery 23.3%)C₂H₄ residual in product gas:  ~0.2% N₂ residual in product gas:  ~1.2%Flow of hydrogen gas selectively 0.96 Nm³/h separated through separationunit

Examples 32 to 59

CNTs were prepared in the same manner as in Examples 1 to 28 except thata metal (Pd) membrane gas separation unit (Pd/alumina stainless steelmembrane) was used instead of the hydrogen PSA unit. The H₂ separationefficiency (%) and CNT yield (%) thus obtained are shown in Table 8below.

Example 60

CNTs were prepared in the same manner as in Example 29 except that ametal (Pd) membrane gas separation unit (Pd/alumina stainless steelmembrane) was used instead of the hydrogen PSA unit.

The following Table 7 shows flow rate and composition of the mixed gasdischarged from the reactor of Example 60. The following Table 8 showsflow rate and composition of the hydrogen gas separated and dischargedthrough the metal (Pd) membrane gas separation unit of Example 60.

TABLE 7 Gas (mixed gas) present in reactor outlet Flow of gas present inreactor 3.63 Nm³/h outlet Hydrogen in feed gas: 78.1% C₂H₄ in feed gas: 4.5% N₂ in feed gas: 17.4%

TABLE 8 Filter (Pd metal membrane) outlet gas (separated and dischargedhydrogen gas) Hydrogen in product gas: >98.6% (hydrogen recovery 33.04%)C₂H₄ residual in product gas:  ~0.2% N₂ residual in product gas:  ~1.2%Flow of hydrogen gas selectively 0.96 Nm³/h separated through separationunit

Example 61

CNTs were prepared in the same manner as in Example 30 except that ametal (Pd) membrane gas separation unit (Pd/alumina stainless steelmembrane) was used instead of the hydrogen PSA unit.

The following Table 9 shows flow rate and composition of the mixed gasdischarged from the reactor of Example 61. The following Table 10 showsflow rate and composition of the hydrogen gas separated and dischargedthrough the metal (Pd) membrane gas separation unit of Example 61.

TABLE 9 Gas present in reactor outlet (mixed gas) Flow of gas present inreactor 3.99 Nm³/h outlet Hydrogen in feed gas: 82.4% C₂H₄ in feed gas:2.94% N₂ in feed gas: 14.7%

TABLE 10 Filter (Pd metal membrane) outlet gas (separated and dischargedhydrogen gas) Hydrogen in product gas: >98.6% (hydrogen recovery 28.6%)C₂H₄ residual in product gas:  ~0.2% N₂ residual in product gas:  ~1.2%Flow of hydrogen gas selectively 0.96 Nm³/h separated through separationunit

Example 62

CNTs were prepared in the same manner as in Example 31 except that ametal (Pd) membrane gas separation unit (Pd/alumina stainless steelmembrane) was used instead of the hydrogen PSA unit.

The following Table 11 shows flow rate and composition of the mixed gasdischarged from the reactor in Example 62. The following Table 12 showsflow rate and composition of the hydrogen gas separated and dischargedthrough the metal (Pd) membrane gas separation unit in Example 62.

TABLE 11 Gas (mixed gas) present in reactor outlet Flow of gas presentin reactor 4.78 Nm³/h outlet Hydrogen in feed gas: 84.02%  C₂H₄ in feedgas:  3.1% N₂ in feed gas: 12.9%

TABLE 12 Filter (Pd metal membrane) outlet gas (separated and dischargedhydrogen gas) Hydrogen in Product Gas: >98.6% (hydrogen recovery 23.3%)C₂H₄ Residual in Product Gas:  ~0.2% N₂ Residual in Product Gas:  ~1.2%Flow of hydrogen gas selectively 0.96 Nm³/h separated through separationunit

Comparative Example 1

CNTs were produced in the same manner as in Example 2 above except that100% of the mixed gas separated by the cyclone was re-circulated withoutpassing through the hydrogen PSA unit and only ethylene (C₂H₄)corresponding to 85% of the initial feed amount was added to thereaction gas supply pipe.

The continuous operation was tried in the reaction, but 2 moles ofhydrogen (H₂) produced as a reaction byproduct per one mole of ethylenewas continuously accumulated in the reactor, thus causing an increase inpressure in the reactor and interfering with smooth injection of C₂H₄and thereby making stable operation impossible within 20 minutes.

Comparative Example 2

CNTs were produced in the same manner as in Example 2 above except thatthe same composition and content of reaction gas as in Example 2 wascontinuously supplied without the hydrogen PSA unit and recirculationpipe.

This reaction exhibited increases in consumption levels of ethylene,nitrogen and hydrogen by 3-7 times, 80 to 100 times, and 100 times ormore, respectively, as compared to Example 2 and thus considerablyincreasing CNT production costs.

After one hour of reaction, CNTs collected in the CNT collector had ayield of 830% and a carbon source conversion rate of 80% based oncatalyst input.

Experimental Example

The reaction conditions, carbon source conversion rate and CNT yield ofExamples 1 to 28 and 32 to 59 were measured in accordance with thefollowing methods. The results thus obtained are shown in Tables 13 and14 below.

-   -   Carbon source conversion rate (%) was obtained by measuring an        amount of ethylene gas supplied to the reactor and an amount of        ethylene gas discharged from the outlet of the reactor by gas        chromatography and calculating the conversion rate in accordance        with Equation 1 below:

Carbon source conversion rate=(flow of ethylene gas injected to reactor(gmol/hr)−flow of ethylene discharged from reactor (gmol/hr))×100/flowof ethylene injected to reactor (gmol/hr)  [Equation 1]

-   -   CNT Yield (%) was obtained from the difference between a weight        of catalyst and a weight of CNTs measured after the reaction        using a precise electronic scale in accordance with Equation 2        below:

Catalyst Yield (%)=(total weight of carbon product recovered (g)−weightof catalyst (g))×100/weight of catalyst (g)

TABLE 13 Amount Gas separation Type of Gas feed efficiency of catalystcomposition Feed H₂ separation CNT yield Ex. reactor Catalyst used C₂H₄H₂ N₂ rate (ml/min) efficiency (%) (%) 1 FBR CoMo/ 5 g 1 1 1 3000 20 9502 Al₂O₃ 5 g 1 2 1 3000 33 1020 3 5 g 1 3 1 3000 28 780 4 5 g 1 4 1 300024 630 5 5 g 1 5 1 3000 20 580 6 Rotary CoMo/ 3 g 1 1 1 1500 25 1050 7kiln Al₂O₃ 3 g 1 2 1 1500 35 850 8 type 3 g 1 3 1 1500 36 680 9 3 g 1 41 1500 24 560 10 3 g 1 5 1 1500 21 490 11 FBR CoMo/ 5 g 1 2 1 3000 341030 12 MgO 5 g 1 3 1 3000 29 810 13 5 g 1 4 1 3000 24 670 14 5 g 1 5 13000 21 560 15 Rotary CoMo/ 3 g 1 1 1 1500 40 980 16 kiln MgO 3 g 1 2 11500 36 840 17 type 3 g 1 3 1 1500 29 690 18 3 g 1 4 1 1500 24 560 19 3g 1 5 1 1500 21 460 20 FBR FeMo/SiO₂ 5 g 1 2 1 3000 33 940 21 5 g 1 3 13000 27 770 22 5 g 1 4 1 3000 23 610 23 5 g 1 5 1 3000 19 530 24 RotaryFeMo/SiO₂ 3 g 1 1 1 1500 40 920 25 kiln 3 g 1 2 1 1500 35 840 26 type 3g 1 3 1 1500 29 670 27 3 g 1 4 1 1500 24 550 28 3 g 1 5 1 1500 20 480

As can be seen from Examples 1 to 31 and Table 13 above, the CNTproduction apparatus and method according to the present inventionincluding the hydrogen PSA unit (Examples 1 to 31) exhibited high carbonsource conversion rate and CNT yield, considerably reduced CNTproduction costs, and produced no waste gas and thus was environmentallyfriendly, as compared to conventional CNT production apparatuses andmethods (Comparative Examples 1 and 2).

TABLE 14 Amount Gas separation Type of Gas feed Feed efficiency (%) ofcatalyst composition rate H₂ separation CNT Ex. reactor Catalyst usedC₂H₄ H₂ N₂ (ml/min) efficiency (%) yield (%) 32 FBR CoMo/ 5 g 1 1 1 300020 940 33 Al₂O₃ 5 g 1 2 1 3000 33 1010 34 5 g 1 3 1 3000 28 780 35 5 g 14 1 3000 24 640 36 5 g 1 5 1 3000 20 570 37 Rotary CoMo/ 3 g 1 1 1 150025 1080 38 kiln Al₂O₃ 3 g 1 2 1 1500 35 840 39 type 3 g 1 3 1 1500 36680 40 3 g 1 4 1 1500 24 560 41 3 g 1 5 1 1500 21 490 42 FBR CoMo/ 5 g 12 1 3000 34 1030 43 MgO 5 g 1 3 1 3000 29 810 44 5 g 1 4 1 3000 24 67545 5 g 1 5 1 3000 21 560 46 Rotary CoMo/ 3 g 1 1 1 1500 40 1020 47 kilnMgO 3 g 1 2 1 1500 36 860 48 type 3 g 1 3 1 1500 29 680 49 3 g 1 4 11500 24 560 50 3 g 1 5 1 1500 21 470 51 FBR FeMo/ 5 g 1 2 1 3000 33 94052 SiO₂ 5 g 1 3 1 3000 27 760 53 5 g 1 4 1 3000 23 610 54 5 g 1 5 1 300019 540 55 Rotary FeMo/ 3 g 1 1 1 1500 40 950 56 kiln SiO₂ 3 g 1 2 1 150035 850 57 type 3 g 1 3 1 1500 29 670 58 3 g 1 4 1 1500 24 550 59 3 g 1 51 1500 20 460

As can be seen from Examples 32 to 62 and Table 14 above, the CNTproduction apparatus and method according to the present inventionincluding the Pd metal membrane (Examples 32 to 62) exhibited highcarbon source conversion rate and CNT yield, considerably reduced CNTproduction costs, and produced no waste gas and thus was environmentallyfriendly, as compared to conventional CNT production apparatuses andmethods (Comparative Examples 1 and 2).

1-14. (canceled)
 15. A method for continuously producing carbonnanotubes comprising: i) reacting a reaction gas containing a carbonsource, a reducing gas and an inert gas with a catalyst to synthesizecarbon nanotubes; ii) separating a mixed gas from the synthesized carbonnanotubes; iii) filtering the separated mixed gas to remove all or partof the reducing gas; iv) recirculating the filtered mixed gas to thereaction i).
 16. The method according to claim 15, wherein the amount ofthe reducing gas removed during the filtration iii) is equivalent to theamount of the reducing gas produced in the reaction.
 17. The methodaccording to claim 15, wherein a molar ratio of the carbon source to thereducing gas in the reaction is 1:0.5 to 1:10.
 18. The method accordingto claim 15, wherein the filtration iii) is carried out using a hydrogenPSA unit.
 19. The method according to claim 15, wherein the filtrationis carried out using a metal membrane gas separation unit.
 20. Themethod according to claim 15, further comprising adding carbon sourcecorresponding to an amount consumed during the reaction to the filteredmixed gas of the recirculation.